How to Install PEX

What You'll Need
PEX tubing
Tubing cutter
Ring crimper
Crimp rings
"Go/No-Go" gauge
Crimp ring removal tool
Measuring tape

To the uninitiated, PEX is cross-linked polyethylene. Though often used in radiant heat installations, it is being used more and more in hot and cold plumbing applications. Unlike rigid copper, it is easy to work with and is approved by almost all local building codes. The tubing is such a new advancement that it hasn't even made it into the books at some local associations.

Through the manufacturing process, links between polyethylene molecules are formed to create bridges, thus giving it the name "crossed linked." This tubing is especially good in hot water applications. Because of its design, PEX is more durable under temperature extremes and chemical attacks, and is more resistant to creep deformation. PEX was developed in the 1960s, and was used mainly in Europe until the 1980s.

Step 1 - Cut the Pex

When cutting PEX, it is imperative that it is a straight, burr-free cut. Measure out the length of PEX you need for installation and cut it with the PEX tubing cutter. These pliers are specially designed for PEX and should always be used.

Step 2 - Set into a Fitting and Crimp

When you have the PEX cut to length, slip a copper crimp ring onto the pipe. Insert the tubing into the piper fitting. It should bottom out on the shoulder of the fitting. Slide the copper crimp ring up so that it is 1/8 to ¼ inch away from the tubing. Crimp the copper crimp ring with the ring crimper, ensuring that the crimper is at a 90-degree angle from the crimp ring. Close the crimp tool fully on the crimp ring.

Step 3 - Check the Connection

Green PEX.

Now, test the crimp with the Go/No-Go gauge. The Go-gauge should slide onto the fitting with ease. It may be tight where the crimping tool has marked the crimping surface during the crimping operation. The No-Go gauge must not slide over the fitting. If it does, the tubing must be recut and the joint made once again.

A bit of finesse is required here. It is very important that the finished joint is done correctly. Look for these problems that will cause a potential leak hazard and an insufficient connection:

  • Ring crimped over the end of the tubing
  • Not enough ribs covered
  • Crimp tool not at 90 degrees
  • Plastic dented and not enough rib coverage
  • Crimp ring not completely covered by crimping tool
  • Ring is distorted with a non-uniform crimp
  • Tubing not squarely cut. Does not cover ribs of fitting

The crimp tool is designed to make accurate crimps. It may need adjustment if you continually make improper connections.

Step 4 - Run the Tubing

PEX will install a bit differently than normal PVC or copper tubing. Allowances must be made for every 10 degrees of change in temperature. PEX contracts 1 inch every 100 feet of pipe with every 10 degrees of temperature change. Offset this by making a loop in the PEX that is no more than 8 times the diameter of the tubing.

You need straps and hangers when installing PEX. It must be supported at least every 32 inches if tubing is installed alongside a joist. If it is placed atop a beam, it should be supported every 6 feet. When run vertically, it requires support at every floor level. When installing, always leave slack in the tubing to allow for contraction. The support hangers should not be so tight that they restrict movement of the PEX.


Why is PEX so good for plumbing needs?

PEX is strong, flexible, and can withstand extremely high and low temperatures. It is easy to install. PEX is highly resistant to chemicals found in the plumbing environment.

Can PEX be installed outside?

At the present time, no. Technology is advancing so that in the near future you may see PEX that is capable of being used outdoors.

Can PEX be used under a cement slab?

Yes. PEX comes in long rolls and can be run under a slab without the use of fittings. If run under a slab, the piping needs to be below the concrete, in the dirt or sand. It should never be in contact with the concrete. When coming out of the concrete or into the room, foam pipe insulation should be installed where the piping comes up through the concrete.

Can PEX be used for underground applications?

PEX is an excellent underground water service piping.

What different joining systems are available?

There are several methods, all involving mechanical fittings. PEX is relatively new in the American market. It is good for installation such as radiant heat systems.